Tree-Set

TreeSet in Java

Overview

The TreeSet class in Java is part of the java.util package and implements the Set interface. It is a NavigableSet, which means it provides methods for navigating and searching elements in a sorted order. The elements are sorted according to their natural ordering or by a comparator provided at the time of creation.

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Characteristics of TreeSet

Feature	Details
Package	java.util
Allows Duplicates	No
Maintains Insertion Order	No (elements are sorted)
Thread-Safe	No
Allows Null Element	No (throws NullPointerException if null is added)
Sorting	Sorts elements based on natural ordering or comparator
Navigable	Yes (supports navigation methods like lower(), ceiling(), higher(), etc.)

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Key Features of TreeSet

• No Duplicates: Ensures that duplicate elements are not allowed.
• Sorted Order: Elements are stored in sorted order either according to their natural order or using a comparator.
• NavigableSet: Provides methods for element navigation like first(), last(), lower(), ceiling(), etc.
• Red-Black Tree: Internally backed by a Red-Black Tree to maintain elements in a sorted manner.

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How to Use TreeSet

Importing TreeSet

import java.util.TreeSet;

Creating a TreeSet

TreeSet<Type> treeSet = new TreeSet<>();

• Example

  TreeSet<String> stringSet = new TreeSet<>();
  TreeSet<Integer> integerSet = new TreeSet<>();

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TreeSet Specific Methods

The TreeSet class provides several methods for efficient set operations while maintaining sorting. Below are some commonly used methods:

Method	Description	Return Type	Example
add(E e)	Adds the specified element to the set if it is not already present.	boolean	treeSet.add("Apple");
contains(Object o)	Returns true if the set contains the specified element.	boolean	treeSet.contains("Banana");
remove(Object o)	Removes the specified element from the set if it is present.	boolean	treeSet.remove("Apple");
clear()	Removes all elements from the set.	void	treeSet.clear();
isEmpty()	Checks if the set is empty.	boolean	treeSet.isEmpty();
size()	Returns the number of elements in the set.	int	treeSet.size();
toArray()	Converts the set to an array.	Object[]	Object[] array = treeSet.toArray();
first()	Returns the first (lowest) element in the set.	E	treeSet.first();
last()	Returns the last (highest) element in the set.	E	treeSet.last();
lower(E e)	Returns the greatest element strictly less than the specified element.	E	treeSet.lower("Banana");
ceiling(E e)	Returns the least element greater than or equal to the specified element.	E	treeSet.ceiling("Banana");
pollFirst()	Retrieves and removes the first (lowest) element.	E	treeSet.pollFirst();
pollLast()	Retrieves and removes the last (highest) element.	E	treeSet.pollLast();

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Example Code

import java.util.*;

public class TreeSetExample {
    public static void main(String[] args) {
        // Create a TreeSet
        TreeSet<String> treeSet = new TreeSet<>();

        // Add elements
        treeSet.add("Apple");
        treeSet.add("Banana");
        treeSet.add("Cherry");

        // Check size
        System.out.println("Size of the TreeSet: " + treeSet.size());

        // Check if an element exists
        System.out.println("Contains 'Banana': " + treeSet.contains("Banana"));

        // Remove an element
        treeSet.remove("Banana");
        System.out.println("TreeSet after removal: " + treeSet);

        // Retrieve the first and last elements
        System.out.println("First element: " + treeSet.first());
        System.out.println("Last element: " + treeSet.last());

        // Iterate over elements (sorted order)
        System.out.println("TreeSet elements:");
        for (String fruit : treeSet) {
            System.out.println(fruit);
        }

        // Convert to array
        Object[] array = treeSet.toArray();
        System.out.println("Array from TreeSet: " + Arrays.toString(array));

        // Clear the TreeSet
        treeSet.clear();
        System.out.println("Is TreeSet empty? " + treeSet.isEmpty());
    }
}

For more: TreeSetDataStructure.java